package com.example;

public class BookTest {
    /* 用来记录当前产生到第几个Book类对象 */
    public static int index = 0;

    public static void main(String[] args) {
        new Book();
        new Book();
        new Book();
        System.out.println(new Book().getId());
        System.out.println(C.PAI);
        // C.PAI = 3;// 不能修改
    }
}
